Adjustable ventilation openings in MEMS structures

ABSTRACT

A MEMS structure and a method for operation a MEMS structure are disclosed. In accordance with an embodiment of the present invention, a MEMS structure comprises a substrate, a backplate, and a membrane comprising a first region and a second region, wherein the first region is configured to sense a signal and the second region is configured to adjust a threshold frequency from a first value to a second value, and wherein the backplate and the membrane are mechanically connected to the substrate.

TECHNICAL FIELD

The present invention relates generally to an adjustable ventilationopening in a MEMS structure and a method for operating a MEMS structure.

BACKGROUND

In general, microphones are manufactured in large numbers at low cost.Due to these requirements, microphones are often produced in silicontechnology. Microphones are produced with different configurations fortheir different field of applications. In one example, microphonesmeasure the change in capacity by measuring the deformation ordeflection of the membrane relative to a counter electrode. Themicrophone is typically operated a setting a bias voltage to anappropriate value.

A microphone may have operation and other parameters such assignal-to-noise ratio (SNR), rigidity of the membrane or counterelectrode, or diameter of the membrane which often are set by themanufacturing process. In addition, a microphone may have differentcharacteristics based on different materials used in the manufacturingprocess.

SUMMARY OF THE INVENTION

In accordance with an embodiment of the present invention, a MEMSstructure comprises a substrate, a backplate, and a membrane comprisinga first region and a second region, wherein the first region isconfigured to sense a signal and the second region is configured toadjust a threshold frequency from a first value to a second value, andwherein the backplate and the membrane are mechanically connected to thesubstrate.

In accordance with another embodiment of the present invention, a MEMSstructure comprises a substrate, a backplate, and a membrane comprisingan adjustable ventilation opening. The backplate and the membrane aremechanically connected to the substrate.

In accordance with an embodiment of the present invention, a method foroperating a MEMS structure comprises sensing an acoustic signal bymoving a sensing region of a membrane relative to a backplate andopening or closing an adjustable ventilation opening in the membrane ifa high energy signal is detected.

In accordance with an embodiment of the present invention, a methodcomprises sensing an acoustic signal by moving a membrane relative to abackplate, and opening or closing an adjustable ventilation opening inthe membrane if an application setting of the MEMS structure is changed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 a shows a top view of a MEMS structure;

FIG. 1 b shows a detailed perspective view of a connection region of aMEMS structure;

FIG. 1 c shows a cross sectional view of a connection region of a MEMSstructure;

FIGS. 2 a-2 c show cross-sectional views of an embodiment of anadjustable ventilation opening;

FIG. 2 d shows a top view of an embodiment of an adjustable ventilationopening;

FIG. 2 e shows a diagram for a corner or threshold frequency;

FIGS. 3 a-3 d show embodiments and configuration of an adjustableventilation opening;

FIG. 4 a shows a cross-sectional view of an embodiment of a MEMSstructure, wherein the membrane is pulled toward the backplate;

FIG. 4 b shows a cross-sectional view of an embodiment of a MEMSstructure, wherein the membrane is pulled toward the substrate;

FIG. 5 a shows a cross-section view of an embodiment of a MEMSstructure;

FIG. 5 b shows a top-view of an embodiment of the MEMS structure of FIG.5 a;

FIG. 6 a shows a cross-section view of an embodiment of a none actuatedMEMS structure;

FIG. 6 b shows a cross-section view of an embodiment of an actuated MEMSstructure;

FIG. 7 a shows a cross-section view of an embodiment of a none actuatedMEMS structure;

FIG. 7 b shows a cross-section view of an embodiment of an actuated MEMSstructure;

FIG. 7 c shows a top-view of an embodiment of the MEMS structure of FIG.7 a;

FIG. 8 a shows a flow chart of an operation of a MEMS structure, whereinthe adjustable ventilation opening is originally closed;

FIG. 8 b shows a flow chart of an operation of a MEMS structure, whereinthe adjustable ventilation opening is originally open;

FIG. 8 c shows a flow chart of an operation of a MEMS structure, whereinthe adjustable ventilation opening is opened to switch from a firstapplication setting to a second application setting; and

FIG. 8 d shows a flow chart of an operation of a MEMS structure, whereinthe adjustable ventilation opening is closed to switch from a firstapplication setting to a second application setting.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to embodiments in aspecific context, namely sensors or microphones. The invention may alsobe applied, however, to other MEMS structures such as pressure sensors,RF MEMS, accelerometers, and actuators.

Microphones are realized as parallel plate capacitor on a chip. The chipis packaged enclosing a given back-volume. A movable membrane vibratesdue to pressure differences such as acoustic signals. The membranedisplacement is translated into an electrical signal using capacitivesensing.

FIG. 1 a shows a top view of a MEMS device 100. A backplate or counterelectrode 120 and a movable electrode or membrane 130 are connected viaconnection regions 115 to the substrate 110. FIGS. 1 b and 1 c showdetailed perspective views of one connection regions 115 of the MEMSdevice 100. A backplate or counter electrode 120 is arranged over amembrane or movable electrode 130. The backplate 120 is perforated toavoid or mitigate damping. The membrane 130 comprises a ventilation hole140 for low frequency pressure equalization.

In the embodiment of FIGS. 1 a-1 c the membrane 130 is mechanicallyconnected to the substrate 110 in the connection regions 115. In theseregions 115 the membrane 130 cannot move. The backplate 120 is alsomechanically connected to the substrate 110 in the connection region115. The substrate 110 forms a rim 122 to provide space for theback-volume. The membrane 130 and the backplate 120 are connected to thesubstrate at or close to the rim 122. In this embodiment the rim 122 andthe membrane 120 form a circle. Alternatively, the rim 122 and themembrane 120 may comprise a square or may comprise any other suitablegeometrical form.

In general, designing and manufacturing a sensor requires a highsignal-to-noise ratio (SNR). Among other things, this can be achievedwhen the change in capacitances to be measured is as great as possibleand when the parasitic capacitances are as small as possible. Thegreater the parasitic portion of the capacitance is relative to theoverall capacitance, the smaller the SNR.

The compliance of the back-volume and the resistance of the ventilationpath through the ventilation hole define the RC constant of the sensor.If the ventilation hole is large the corner frequency is a relativelyhigh frequency and if the ventilation hole is small the corner frequencyis a relatively lower frequency. Both back-volume and the diameter ofthe ventilation hole are given by construction and hence the cornerfrequency is given by construction. Accordingly, the corner frequencycannot be changed during operation.

A problem with a fixed size ventilation hole is that high energeticsignals that have a frequency higher than the corner frequency of theventilation hole distort or overdrive the sensor even with theapplication of electrical filters. Moreover, if a sensor is used formore than one application two sensors must be integrated into one sensorsystem which doubles the system costs.

An embodiment of the invention provides tunable ventilation openings ina MEMS structure. The tunable ventilation openings may be switchedbetween an open position and a closed position. The tunable ventilationholes may also be set in an intermediate position. Another embodiment ofthe invention provides a variable ventilation opening cross-section. Anembodiment of the invention provides a tunable ventilation opening in asensing region close to a rim of the substrate. A further embodimentprovides a tunable ventilation opening in a tuning region outside thesensing region of the membrane.

FIGS. 2 a-2 c show a cross sectional views of a backplate orcounter-electrode 250 and a membrane or movable electrode 230 having anair gap 240 between them. The backplate 250 is perforated 252 and themembrane 230 comprises an adjustable ventilation opening 238. FIG. 2 dshows a top view of this arrangement with the circles indicating theperforated back plate 250, 252 and dark plane being the underlyingmembrane 230. In this embodiment the movable portion 237 of theadjustable ventilation hole 238 is formed as a U shaped slot 239. Theadjustable ventilation opening 238 may comprise of rectangular, squareor semicircle form. Alternatively, the adjustable ventilation opening238 may comprise any geometrical form as long as the form is able toprovide a ventilation path. The movable portion 237 of the adjustableventilation opening 238 may be a cantilever, a bridge or a springsupported structure.

The FIG. 2 a shows a configuration where the actuation voltage (biasvoltage) V_(bias)=0. The adjustable ventilation opening 238 is closedforming a small slot 239 in the membrane 230. No actuation voltageprovides a minimal ventilation path and therefore a low thresholdfrequency. The adjustable ventilation opening 238 is in a closed or OFF(non-activated) position. An example of such a low threshold frequencycan be seen as frequency “A” in FIG. 2 e.

FIG. 2 b shows a configuration where the actuation voltage V_(bias) isincreased, i.e. is different than 0 V but lower than the pull-in voltageV_(pull-in). The adjustable ventilation opening 238 opens and provides alarger ventilation path than in the configuration of FIG. 2 a. Thethreshold frequency can be seen as frequency “B” in FIG. 2 e. It isnoted that adjustable ventilation opening 238 may provide a sizableventilation path when displacement of the movable portion 237 is largerthan the thickness of the membrane 230.

FIG. 2 c shows a configuration where the actuation voltage V_(bias) islarger than pull-in voltage V_(pull-in). The adjustable ventilationopening 238 is completely open and a large ventilation path is created.The threshold frequency can be seen as frequency “C” in FIG. 2 e. Byadjusting the actuation voltage the RC constant can be decreased orincreased and the threshold frequency can be set according to a desiredvalue. It is noted that the adjustable ventilation opening may alreadyopen completely for actuation voltages below the pull-in voltage.

Referring now to FIG. 2 e, in one embodiment the threshold frequency “A”may be about 10-50 Hz and may be moved to about 200-500 Hz as thresholdfrequency “C.” Alternatively, the threshold frequency in “A” is about10-20 Hz and is moved to about 200-300 Hz in “C.”

The threshold frequency in position “A” may also depend on the number ofadjustable ventilation openings and the gap distance a slot forms in themembrane. The threshold frequency in position “A” is higher for a MEMSstructure with more adjustable ventilation openings (e.g. 32 adjustableventilation openings) than for a MEMS structure with less adjustableventilation openings (e.g., 2, 4 or 8 adjustable ventilation openings).The threshold frequency is also higher for MEMS structures with a largerslot gap (larger slot width and/or larger slot length) defining theadjustable ventilation opening than for those with a smaller slot gap.

The embodiment of FIG. 3 a shows a configuration of an actuation voltage(tuning or switching voltage) wherein the actuation voltage is identicalto the sensing bias. The MEMS structure comprises a single electrode onthe backplate 350, an air gap 340 and a membrane 330. The electrode ofthe backplate 350 is set to an actuation potential and the membrane 330is set to ground. The adjustable ventilation opening 338 is closed witha low actuation voltage (OFF position) and open with a high actuationvoltage (ON position). A low actuation voltage results in a low corneror threshold frequency and a low sensitivity of the MEMS structure, anda high actuation voltage results in a high corner or threshold frequencyand a high sensitivity.

The embodiment of FIG. 3 b shows a configuration wherein the actuationvoltage (tuning or switching voltage) is independent from the sensingbias. The MEMS structure comprises a structured backplate 350, e.g., abackplate that has at least two electrodes, an air gap 340 and amembrane 330. The second electrode 352 of the backplate 350 is set to anactuation potential and the first electrode 351 is set to a sensepotential. The membrane 320 is set to ground. The two electrodes areisolated from each other. For example, the backplate 350 may comprisethe structured electrode and an isolation support 355. The isolationsupport 355 may face toward the membrane 320 or may face away from themembrane 320. The tuning or switching voltage does not influence thesensitivity of the MEMS structure.

The adjustable ventilation opening is 338 closed with a low actuationvoltage (OFF position) and open with a high actuation voltage (ONposition). A low actuation voltage results in a low corner or thresholdfrequency and a high actuation voltage results in a high corner orthreshold frequency. The sense bias is independent from the actuationvoltage and can be kept constant or independently decreased orincreased.

The embodiment of FIG. 3 c shows a configuration of an actuation voltage(tuning or switching voltage) wherein the actuation voltage is identicalto the sensing bias. The MEMS structure comprises a single electrode inthe backplate 350, an air gap 340 and a membrane 330. The adjustableventilation opening 338 is closed with a high actuation voltage (ONposition) and is open with a low actuation voltage (OFF position). Themovable portion 337 of the adjustable ventilation opening 338 touchesthe backplate 350 when activated and is in plane with the rest of themembrane when not activated. A low actuation voltage results in a highcorner or threshold frequency and a low sensitivity of the MEMSstructure, and a high actuation voltage results in low corner orthreshold frequency and a high sensitivity of the MEMS structure. Thebackplate 350 comprises ventilation openings 357 and the movable portion337 of the adjustable ventilation opening 338 comprises ventilationopenings 336. The ventilation openings 336 in the movable portion 337 ofthe adjustable ventilation opening 338 are closed in an ON (oractivated) position. There is no ventilation path through the adjustableventilation opening 338 when the adjustable ventilation opening is inthe ON (or activated) position.

The embodiment of FIG. 3 d shows the actuation voltage (tuning orswitching voltage) wherein the actuation voltage is independent from thesensing bias. This MEMS structure comprises a structured backplate 350,e.g., the backplate may comprise a first electrode 351 and a secondelectrode 352, an air gap 340 and a membrane 330. Alternatively, thestructured backplate 350 may comprise more than two electrodes. Thesecond electrode 352 of the backplate 350 is set to an actuationpotential and the first electrode 351 is set to a sense potential. Themembrane 330 is set to ground. The first electrode 351 and the secondelectrode 352 are isolated from each other. For example, the backplate350 may comprise the structured electrode and an isolation support 355.The isolation support 355 may face toward the membrane 330 or may faceaway from the membrane 330. The tuning or switching voltage does notinfluence the sensitivity of the MEMS structure.

The adjustable ventilation opening is closed with a high actuationvoltage (ON position) and is open with a low actuation voltage (OFFposition). A low actuation voltage (OFF position) results in a highcorner or threshold frequency and a low actuation voltage (ON position)results in a high corner or threshold frequency. The sense bias isindependent from the actuation voltage and can be kept constant orindependently decreased or increased.

The backplate 350 comprises ventilation openings 357 and the movableportion 337 of the adjustable ventilation opening 338 comprises alsoventilation openings 336. The ventilation openings 336 in the adjustableventilation opening 338 are closed in the ON position. There is noventilation path through the ventilation openings 357 of the backplate338 and the ventilation openings 336 of the adjustable ventilationopening 338 when the adjustable ventilation opening 338 is open. Thereis no ventilation path through the ventilation openings 357 of thebackplate 338 and the ventilation openings 336 of the adjustableventilation opening 338 when the adjustable ventilation opening 338 isclosed or in an OFF position.

The embodiment of FIG. 4 a shows a cross-sectional view of a MEMSstructure 400. The MEMS structure comprises a substrate 410. Thesubstrate 410 comprises silicon or other semiconductor materials.Alternatively, the substrate 410 comprises compound semiconductors suchas GaAs, InP, Si/Ge, or SiC, as examples. The substrate 410 may comprisesingle crystal silicon, amorphous silicon or polycrystalline silicon(polysilicon). The substrate 410 may include active components such astransistors, diodes, capacitors, amplifiers, filters or other electricaldevices, or an integrated circuit. The MEMS structure 400 may be astand-alone device or may be integrated with and IC into a single chip.

The MEMS structure 400 further comprises a first insulating layer orspacer 420 disposed over the substrate 410. The insulating layer 420 maycomprise an insulting material such a silicon dioxide, silicon nitride,or combinations thereof.

The MEMS structure 400 further comprises a membrane 430. The membrane430 may be a circular membrane or a square membrane. Alternatively, themembrane 430 may comprise other geometrical forms. The membrane 430 maycomprise conductive material such as polysilicon, doped polysilicon or ametal. The membrane 430 is disposed above the insulating layer 420. Themembrane 430 is physically connected to the substrate 410 in a regionclose to the rim of the substrate 410.

Moreover, the MEMS structure 400 comprises a second insulating layer orspacer 440 disposed over a portion of the membrane 430. The secondinsulating layer 440 may comprise an insulting material such as asilicon dioxide, silicon nitride, or combinations thereof.

A backplate 450 is arranged over the second insulating layer or spacer440. The backplate 450 may comprise a conductive material such aspolysilicon, doped polysilicon or a metal, e.g., aluminum. Moreover, thebackplate 450 may comprise an insulating support or insulating layerregions. The insulating support may be arranged toward or away from themembrane 430. The insulating layer material may be silicon oxide,silicon nitride or combinations thereof. The backplate 450 may beperforated.

The membrane 430 may comprise at least one adjustable ventilationopening 460 as described above. The adjustable ventilation openings 460may comprise a movable portion 465. In one embodiment the adjustableventilation openings 460 are located in a region close to the rim of thesubstrate 410. For example, the adjustable ventilation openings 460 maybe located in the outer 20% of the radius of the membrane 430 or theouter 20% of the distance from a center point to the membrane 430 edgeof a square or a rectangle. In particular, the adjustable ventilationopenings 460 may not be located in a center region of the membrane 430.For example, the adjustable ventilation openings 460 may not be locatedin the inner 80% of the radius or the distance. The adjustableventilation openings 460 may be located in equidistant distances fromeach other along a periphery of the membrane 430.

The embodiment of FIG. 4 a is configured so that the adjustableventilation openings 460 open toward the backplate 450. The membrane 430and the backplate 450 may have any of the configurations as described inFIGS. 2 a-2 d and 3 a-3 d. The backplate 450 is set to a sense voltageV_(sense) and an actuation voltage V_(p) (sense voltage and actuationvoltage can be the same or different as described above) and themembrane 430 is set to ground, or vice versa.

The MEMS structure 400 of the embodiment of FIG. 4 b shows a similarstructure to that of the embodiment in FIG. 4 a. However, theconfiguration is different, e.g., the movable portion 465 of theadjustable ventilation opening 460 is pulled toward the substrate 410.The backplate is set to a sense voltage V_(sense), the substrate is setto the actuation voltage V_(p) and the membrane is set to ground. Inthis configuration of the MEMS structure 400 the actuation voltage(tuning or switching voltage) is independent of the sensing voltage.

The embodiment of FIG. 5 a shows a cross sectional view and FIG. 5 cshows a top view of a MEMS structure 500 having a membrane 530 extendingover a portion of the substrate 510 and outside a sensing region 533.The MEMS structure 500 comprises a substrate 510, a connection region520, a membrane 530 and a backplate 540 which comprise similar materialsas described with respect to the embodiment in FIG. 4 a. The membrane530 comprises a sensing region 533 and a tuning region 536. The sensingregion 533 is located between the opposite rims of the substrate 510 orbetween the opposite connection regions 520. The tuning region 533extends over a portion of the substrate 510 and is located outside thesensing region 533. The sensing region 536 may be located on a firstside of the connection region 520 and the tuning region 533 may belocated on a second side of the connection region 520. A recess 515(under etch) is formed between the membrane 530 and the substrate 510 inthe tuning region 536. The backplate 540 overlies only the sensingregion 533 but not the tuning region 536 of the membrane 530. Thebackplate 540 may be perforated. The backplate 540 is set to a biasvoltage V_(sense), the substrate 510 is set to a tuning voltage V_(p)and the membrane is set to ground. In this configuration of the MEMSstructure 500 the tuning voltage is independent of the sensing voltage.

The tuning region 536 of the membrane 530 comprises at least oneadjustable ventilation openings 538 which provide a ventilation path ina non-actuated position (OFF position) and which does not provide aventilation path in an actuated position (ON positioni). Thenon-actuated or open position (OFF position) is a position wherein theadjustable ventilation openings 538 are in the same plane as themembrane 530 in the sensing region 533 in in its resting position. Theactuated or closed position (ON position) is a position wherein theadjustable ventilation openings 538 are pressed against the substrate510 and the ventilation path is blocked. Intermediate positions may beset by pulling the adjustable ventilation openings 538 towards thesubstrate 510 but where the adjustable ventilation openings 538 are notpressed against the substrate 510. It is noted that the sensing region533 may or may not comprise adjustable ventilation openings 538.

The embodiment of FIGS. 6 a and 6 b show a cross sectional view of aMEMS structure 600 having a membrane 630 extending over a portion of thesubstrate 610 outside a sensing region 633. The MEMS structure 600comprises a substrate 610, a connection region 620, a membrane 630 and abackplate 640 which comprise similar materials as described with respectto the embodiment in FIG. 4 a. The membrane 630 comprises a sensingregion 633 and a tuning region 636. The sensing region 633 is locatedbetween the opposite rims of the substrate 610 or between the oppositeconnection regions 620. The tuning region 636 extends over a portion ofthe substrate 610 and is located outside the sensing region 633. Thesensing region 633 may be located on a first side of the connectionregion 620 and the tuning region 636 may be located on a second side ofthe connection region 620. A recess 615 is formed between the membrane630 and the substrate 610 in the tuning region 636. The backplate 640overlies the sensing region 633 and the tuning region 636 of themembrane 630. The backplate 640 may be perforated in the sensing region633 and the tuning region. Alternatively, the backplate 640 may beperforated in the sensing region 633 but not in the tuning region 636.The backplate 640 comprises a first electrode 641 and a second electrode642. Alternatively, the backplate 640 comprise more than two electrodes.The first electrode 641 is isolated from the second electrode 642. Thefirst electrode 641 is disposed in the sensing region 633 and the secondelectrode 642 is disposed in the tuning region 636. The first electrode641 is set to a bias voltage V_(sense), and the second electrode 642 isset to the tuning voltage V_(p). The membrane 630 is set to ground. Inthis configuration of the MEMS structure 600 the tuning voltage isindependent of the sensing voltage.

The tuning region 636 of the membrane 630 comprises one or moreadjustable ventilation openings 638 which provide a ventilation path inan non-actuated position (OFF position) in FIG. 6 a and which does notprovide a ventilation path in an actuated position (ON position) in FIG.6 b. The open position or non-actuated (OFF position) is a positionwherein the adjustable ventilation openings 638 are in the same plane asthe membrane 630 in the sensing region 633 in its resting position. Theclosed position or actuated position (ON position) is a position whereinthe adjustable ventilation openings 638 are pressed against thebackplate 640 and the ventilation path is blocked. The MEMS structure600 provides a ventilation path and a high corner frequency when it isnot in an actuated position (OFF position). The MEMS structured 600provides a closed ventilation path and a low corner frequency when it isin an actuated position (ON position). Intermediate positions may be setby pulling the adjustable ventilation openings 638 toward the backplate640 but where the adjustable ventilation openings 638 are not pressedagainst the backplate 640. It is noted that the sensing region 633 mayor may not comprise adjustable ventilation openings 638.

The backplate 640 comprises ventilation openings 639 and the membrane630 comprises adjustable ventilation openings 638 in the tuning region636. In one embodiment the ventilation openings 639 and the adjustableventilation openings 638 are reversely aligned with respect to eachother.

The embodiment of FIGS. 7 a and 7 b show a cross sectional view and FIG.7 c shows a top view of a MEMS structure 700 having a membrane 730extending over a portion of the substrate 710 and outside a sensingregion 733. The MEMS structure 700 comprises a substrate 710, aconnection region 720, a membrane 730 and a backplate 740 which comprisesimilar materials as described with respect to embodiment of FIG. 4 a.The backplate 740 may comprise a sensing backplate (e.g. circular orrectangle) 741 and a backplate bridge 742.

The membrane 730 comprises a sensing region 733 and a tuning region 736.The sensing region 733 is located between the opposite rims of thesubstrate 710 or between the opposite connection regions 720. The tuningregion 733 extends over a portion of the substrate 710 and is locatedoutside the sensing region 733. The sensing region 736 may be located ona first side of the connection region 720 and the tuning region 733 maybe located on a second side of the connection region 720. A recess 715(under etch) is formed between the membrane 730 and the substrate 710 inthe tuning region 736. The membrane 730 comprises an adjustableventilation opening 738 formed by a slot 735. The slot 735 forms amovable portion as described in FIGS. 2 a-2 c for the adjustableventilation opening 738

The backplate 740 overlies the sensing region 733 and the tuning region736 of the membrane 730. For example, the sensing backplate 741 (firstelectrode) overlies the sensing region 733 and the backplate bridge 742(second electrode) overlies the tuning region 736. Alternatively, thebackplate 740 comprise more than two electrodes. The first electrode 741is isolated from the second electrode 742. The first electrode 741 isset to a bias voltage V_(sense) and second electrode 742 is set to atuning voltage V_(p). The membrane 730 is set to ground. In thisconfiguration of the MEMS structure 700 the tuning voltage isindependent of the sensing voltage. The backplate 740 may be perforatedin the sensing region 733 and the tuning region 736. Alternatively, thebackplate 740 may be perforated in the sensing region 733 but not in thetuning region 736. The backplate bridge 742 comprises ventilationopenings 749.

The tuning region 736 of the membrane 730 comprises one or moreadjustable ventilation openings 738 which provide a ventilation path inan actuated position (ON position) in FIG. 7 b and which do not providea ventilation path in a non-actuated position (OFF position) in FIG. 7a. The closed or non-actuated position (OFF position) is a positionwherein the adjustable ventilation openings 738 are in the same plane asthe membrane 730 in the sensing region 733 in its resting position. Theopen or actuated position (ON position) is a position wherein theadjustable ventilation openings 738 are pressed against the backplate740 and the ventilation path is open. The MEMS structure 700 provides aventilation path and a high corner frequency when it is in an actuatedposition (ON position). The MEMS structured 700 provides a closedventilation path and a low corner frequency when it is in none actuatedposition (OFF position). Intermediate positions may be set by pullingthe adjustable ventilation openings 738 toward the backplate 740 butwhere the adjustable ventilation openings 738 are not pressed againstthe backplate 740. It is noted that the sensing region 733 may or maynot comprise adjustable ventilation openings 738.

FIG. 8 a shows an embodiment of operating a MEMS structure. In a firststep 810, an acoustic signal is sensed by moving a membrane relative toa backplate. The adjustable ventilation opening is in a closed position.In a next step 812, a high energy signal is detected. The adjustableventilation opening is moved from a closed position to an open position,814. The open position may be a completely open position or a partiallyopen position.

FIG. 8 b shows an embodiment of operating a MEMS structure. In a firststep, 820, an acoustic signal is sensed by moving a membrane relative toa backplate. The adjustable ventilation opening is in an open position.In a next step 822, a high energy signal is detected. The adjustableventilation opening is moved from the open position to a closedposition, 824. The closed position may be a completely closed positionor a partially closed position.

FIG. 8 c shows an embodiment of operating a MEMS structure. In a firststep, 830, the MEMS structure is in a first application setting sensingacoustic signals by moving a membrane relative to a backplate. Theadjustable ventilation opening is in a closed position. In a secondstep, 832, the MEMS structure is in a second application setting sensingacoustic signals by moving a membrane relative to the backplate. Theadjustable ventilation opening is moved from a closed position to anopen position. The open position may be a completely open position or apartially open position.

FIG. 8 d shows an embodiment of operating a MEMS structure. In a firststep, 840, the MEMS structure is in a first application setting sensingacoustic signals by moving a membrane relative to a backplate. Theadjustable ventilation opening is in an open position. In a second step,842, the MEMS structure is in a second application setting sensingacoustic signals by moving a membrane relative to the backplate. Theadjustable ventilation opening is moved from an open position to anclosed position. The closed position may be a completely closed positionor a partially closed position.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A MEMS structure comprising: a substrate; abackplate; and a membrane comprising a first region and a second region,wherein the first region is configured to sense a signal and the secondregion is configured to adjust a threshold frequency from a first valueto a second value, wherein the backplate comprises a first electrode anda second electrode, wherein the first region of the membrane correspondsto the first electrode, and wherein the second region of the membranecorresponds to the second electrode, and wherein the backplate and themembrane are mechanically connected to the substrate.
 2. The MEMSstructure according to claim 1, wherein the first region is located in acenter region of the membrane, and wherein the second region is locatedin a periphery region of the membrane.
 3. The MEMS structure accordingto claim 1, wherein the first region is located over an area encompassedby a rim, and wherein second region overlies a portion of the substrate.4. The MEMS structure according to claim 1, wherein the backplate iselectrically connected to a sense voltage V_(sense), wherein thesubstrate is electrically connected to a tuning voltage V_(tune), andwherein the membrane is electrically connected to ground.
 5. The MEMSstructure according to claim 1, wherein the backplate is electricallyconnected to a sense bias V_(sense), and to a tuning voltage V_(tune),and wherein the membrane is electrically connected to ground.
 6. TheMEMS structure according to claim 1, wherein the backplate comprises afirst region and a second region, wherein the first region of thebackplate corresponds to the first region of the membrane, wherein thesecond region of the backplate corresponds to the second region of themembrane, wherein the first region of the backplate is electricallyconnected to a sense voltage V_(sense), wherein the second region of thebackplate is electrically connected to a tuning voltage V_(tune), andwherein the membrane is connected to ground.
 7. A MEMS structurecomprising: a substrate; a backplate; and a membrane comprising anadjustable ventilation opening, wherein the backplate and the membraneare mechanically connected to the substrate, wherein the backplate is astructured backplate having a first electrode and a second electrode,and wherein the adjustable ventilation opening corresponds to the secondelectrode but not to the first electrode.
 8. The MEMS structureaccording to claim 7, wherein the membrane comprises a central regionand an outer region, the out region encompassing the central region, andwherein the adjustable ventilation opening is located in the outerregion.
 9. The MEMS structure according to claim 7, wherein theadjustable ventilation opening is configured to move toward thesubstrate if actuated.
 10. The MEMS structure according to claim 7,wherein the adjustable ventilation opening is configured to move towardthe backplate if actuated.
 11. The MEMS structure according to claim 7,wherein the adjustable ventilation opening comprises a cantilever, andwherein the cantilever is without ventilation openings.
 12. The MEMSstructure according to claim 7, wherein the adjustable ventilationopening comprises a cantilever, and wherein the cantilever comprisesventilation openings.
 13. The MEMS structure according to claim 7,wherein the adjustable ventilation opening comprises a plurality ofadjustable ventilation openings, and wherein the adjustable ventilationopenings are disposed in a periphery of the membrane placed inequidistant distances.
 14. A MEMS structure comprising: a substrate; abackplate; and a membrane comprising a first region and a second region,wherein the first region is configured to sense a signal and the secondregion is configured to adjust a threshold frequency from a first valueto a second value, wherein the backplate and the membrane aremechanically connected to the substrate, and wherein the backplate iselectrically connected to a sense voltage V_(sense), and to a tuningvoltage V_(tune), and wherein the membrane is electrically connected toground.
 15. A MEMS structure comprising: a substrate; a backplate; and amembrane comprising a first region and a second region, wherein thefirst region is configured to sense a signal and the second region isconfigured to adjust a threshold frequency from a first value to asecond value, wherein the backplate and the membrane are mechanicallyconnected to the substrate, and wherein the backplate comprises a firstregion and a second region, wherein the first region of the backplatecorresponds to the first region of the membrane, wherein the secondregion of the backplate corresponds to the second region of themembrane, wherein the first region of the backplate is electricallyconnected to a sense voltage V_(sense), wherein the second region of thebackplate is electrically connected to a tuning voltage V_(tune), andwherein the membrane is connected to ground.
 16. A MEMS structurecomprising: a substrate; a backplate; and a membrane comprising anadjustable ventilation opening, wherein the backplate and the membraneare mechanically connected to the substrate, wherein the adjustableventilation opening comprises a cantilever, and wherein the cantileveris without ventilation openings.
 17. A MEMS structure comprising: asubstrate; a backplate; and a membrane comprising an adjustableventilation opening, wherein the backplate and the membrane aremechanically connected to the substrate, wherein the adjustableventilation opening comprises a cantilever, and wherein the cantilevercomprises ventilation openings.